1. Field of the Invention
The invention generally relates to the field of selectively preparing highly pure lithium carbonate and various other highly pure lithium containing compounds.
2. Description of the Related Art
Lithium carbonate (Li2CO3) is typically produced commercially from two sources: (1) the extraction from pegmatite mineral sources such as spodumene, lithiophyllite, or lepidolite, which can be obtained through traditional mining; and (2) extraction from lithium-containing brines, such as those found in the Salar de Atacama in Chile, Silver Peak Nev., Salar de Uyuni in Bolivia, or the Salar de Hombre Muerte in Argentina. There are alternative brine sources, such as, geothermal, oilfield, Smackover, and relict hydrothermal brines. These brines, however, have not previously been commercially exploited.
There are a number of commercial applications for lithium carbonate including: use as an additive in aluminum smelting (molten salt electrolysis); enamels and glasses; to control manic depression (when used in its purer forms); and in the production of electronic grade crystals of lithium niobate, tantalite and fluoride. High purity lithium carbonate is required for the fabrication of several materials in lithium ion batteries, such as, the cathode materials and electrolyte salts, and also in more avant-garde secondary batteries which require highly pure lithium metal.
In the case of lithium ion batteries, purified lithium carbonate may be required for the fabrication of the cathode, as well as in the active materials for cathodes such as, and without limitation, lithium cobalt oxide, lithium manganese oxide or lithium iron phosphate, as well as, mixed metal oxides, such as, lithium cobalt nickel manganese oxide.
Several processes currently exist for the removal of lithium from lithium chloride-rich brines or other lithium containing liquids, however, none of the currently employed methods are suitable for the production of lithium carbonate containing low levels of magnesium and calcium, thus limiting the ability of the lithium carbonate to be used as a battery grade lithium product without first undergoing further purification. Methods for extracting lithium carbonate from mineral sources, such as spodumene or lithium aluminum silicate ore (LiAlSi2O6), similarly produce materials that lack sufficient purity for use in batteries. The purity of the resulting material using these processes is not sufficiently pure for battery grade lithium metal production, or for pharmaceutical grade lithium carbonate. Therefore, there is a need for a method for extracting lithium from lithium-containing brines and to produce lithium salts such as chloride and carbonate of sufficient purity to produce high-purity lithium metal.